He was overthrown in a bloodless military coup in 2006 and has lived abroad since then, but he said Tuesday he was looking into returning in coming months.
"The court and police had already issued arrest warrants on him so once he arrives back to Thailand the authorities concerned are duty-bound by law to arrest him," Samphan said.
Room for negotiations
Tony Cheng, reporting for Al Jazeera from northern Thailand, said the statement was unlikely to be definitive.
"Although the attorney-general is saying today that these charges do need to be faced and Mr Thaksin will be arrested if he comes back, there's probably quite a lot of room for negotiation," he said.
The supreme court issued arrest warrants for Thaksin and his wife in August over separate corruption charges linked to a real-estate deal in 2003.
Then, in September, a Thai criminal court issued another arrest warrant against the former first couple over charges tied to alleged fraudulent filings to the Securities and Exchange Commission in 2003.
Thaksin and his wife deny the charges and say they are politically motivated.
The Thaksin-allied People Power Party (PPP), which claimed victory in elections on Sunday with 233 of the 480 seats in parliament, had promised to allow Thaksin back home.
Terms for return
"Mr Thaksin's supporters have been given a fairly strong mandate in the elections over the weekend with a very large majority," Cheng reported.
"The PPP are now looking to put together a coalition government ... and I think one of the things they will be trying to agree to are the terms on which Mr Thaksin could return to the country."
Nevertheless, Samphan said the results of the election had no bearing on the legal cases against the former prime minister.
"The case is gone too far for a reversal," he said.
The PPP says it has already gathered enough support from smaller parties to form a coalition. But analysts say horse-trading continues and that it is too early to declare the pro-Thaksin group as Thailand's next government.